Targeted by the marketing effort are Windows 7 and Windows 8.1 users, who will be allowed to get the new operating for free -- as long as they do so within a year after its release. That means users will have until July 29, 2016 to make the move -- although Microsoft clearly wants them to do so sooner rather than later.

Here's what Windows 7 and Windows 8.1 users can expect:

The campaign revolves around the "Get Windows 10" application, which lets consumers and small businesses "reserve" a copy of the upcoming OS. (The app was rolled out earlier this year as a "Recommended" update in Windows Update and automatically installed on PCs where the default settings for Windows Update were unchanged.)

Microsoft last month made the app a Recommended update for all eligible devices, pushing it to more PCs in preparation for today's announcement. It will appear after a user logs in, and refreshes itself daily.

The Get Windows 10 app is triggered by clicking on the small Windows logo icon in the notification section of the task bar. At that point, users are allowed to "reserve" a copy of Windows 10.

Users who want to get rid of the task bar icon can select "Customize" from the notification area, choose "GWX" and then set it to "Hide icon and notifications." Or if they want to remove the app entirely to avoid the nag campaign should uninstall KB3035583 from the Windows Update pane.

The version served up to customers depends on what they're already running: Windows 7 Starter, Windows 7 Home Basic, Windows 7 Home Premium and Windows 8.1 will get Windows 10 Home. Those using Windows 7 Professional, Windows 7 Ultimate, Windows 8.1 Pro for Students and Windows 8.1 Pro will get Windows 10 Pro.

Although Microsoft at one point indicated that users of non-genuine copies of Windows would be eligible for the free upgrade, the company backed away from that stance last month. Those users won't see the notifications or the Get Windows 10 app.

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